Liver is composed of two major cell types, the tissue parenchymal or hepatocytes, and reticuloendothelial (RE) cells. RE cells make up about 30% of the liver cell population; however, little is known about their metabolism in relation to liver function or in relation to the complete reticuloendothelial system (RES). Hepatic RE cells are also responsible for a major portion of phagocytic capacity in mammals and therefore play an important part in immunological resistances. We propose a project for the biochemical study of cells isolated by iron loading and the development of new techniques for isolating hepatic RE cells. This research includes: (1) evaluation of the iron-loading techniques for isolating RE cells, (2) isolation of hepatic RE cells by digestive perfusion and Ficoll gradient centrifugations, (3) biochemical study of phagocytically active cells and other hepatic RE cells. This will include a qualitative and quantitative study of enzymes from homogeneous Kupffer cells, and a comparative study with the same enzymes isolated from homogeneous hepatocytes. Our procedure for isolating Kupffer cells permits the separation of these from other hepatic RE cells which remained phagocytically inactive. Further investigation of the "inactive" RE cells and a comparison of enzymes from these with those from true Kupffer cells is planned. Enzymes selected for examination will be: (1) those indicated by histo- and cytochemical data to be disproportionately concentrated in liver hepatocytes and RE cells, (2) enzymes which might enable these cells to recognize elements to be phagocytized, and (3) enzymes distinguished in other phagocytes as being important for detoxification and/or digestion of foreign materials.